The recent development of extracorporeal shock wave lithotripsy (ESWL) has greatly reduced the necessity for performing surgery to remove calculi from renal tissue. The occurrence of calculi in tissue frequently occurs in the form of what is commonly known as kidney stones. ESWL has provided a method for fragmenting the calculi with pressure waves so that the stones may be passed in urine without resort to surgery in the majority of cases.
During ESWL treatment the patient is immersed and stabilized in a tub filled with demineralized and degassed warm water. Pressure waves are transmitted through the water and focused on the calculi to pulverize the calculi into particles having the size of sand grains. x-ray fluoroscopes are used to aim the electrodes which generate the pressure waves in the water bath. Typically, the x-ray sources are placed beneath the tub while the fluoroscope image intensifiers are placed in direct contact with the abdomen of the patient at the axial position of the x-ray image. Video monitors provide a picture of the calculi which allows the focus of the pressure waves to be precisely positioned. A forward head portion of the image intensifier penetrates the top level of the water and touches the abdomen of the patient.
Although this procedure has been highly effective for reducing the need for surgery it has been found that the images provided by the fluoroscopes (two fluoroscopes are usually provided to get more precise positioning of the shock waves) have insufficient resolution to provide good aiming of the shock wave generator electrodes once the calculi has been broken down into smaller fragments. Moreover, the resolution is insufficient to access the size of the calculi fragments and whether further exposure to the shock waves is necessary. Presently patients are removed from the water bath after the initial treatment and taken to an x-ray facility to provide high resolution x-ray images of the treated tissue. If further treatment is required, the patient is then reinserted into the water bath and again immobilized therein. The fluoroscope images are compared to the x-ray images so that the shock waves can be precisely focused on the remaining particles.
This procedure is extremely inefficient and expensive and results in under utilization of the machines. Presently, cost of these machines are on the order of $1.7 million dollars. Moreover, patients receive more shocks than would be necessary if the location and size of the fragments could be more precisely determined without removing the patient from the bath. Thus, a need exists for producing high resolution images during ESWL which does not require removal of the patient from the water bath. Furthermore, more precise aiming of the electrode pressure wave generators could reduce the number of shocks which a patient would have to receive thereby decreasing hematuria and renal morbidity (blood in the urine and kidney tissue damage).